In recent years, multilayer interconnection structures have been employed to achieve a high-speed operation and miniaturization of semiconductor devices. However, these structures have raised the problem of wiring delay due to an increase in the overall wiring resistance and parasitic capacitance of the wiring layers.
The use of low resistance wiring material, e.g., copper (Cu), as the interconnection body reduces the wiring resistance. Also, the use of low permittivity or low-k materials, e.g., fluorocarbon (CFx), for the insulating layer reduces the parasitic capacitance. On the other hand, to prevent copper (Cu) from diffusing into the insulating layer, a barrier layer is provided between the interconnection body and the insulating layer. In order to achieve the high-speed operation of semiconductor devices, it is also highly recommended to lower the parasitic capacitance of the barrier layer by using insulating materials such as amorphous carbon (aC).
When fluorocarbon (CFx) is used as the material for the insulating layer, the fluorine contained in the fluorocarbon (CFx) layer causes fluorination reaction at the interface between the fluorocarbon (CFx) layer and the barrier layer made of amorphous carbon (aC). The fluorination reaction is due to subsequent heat treatment processes performed during the manufacturing of semiconductor devices. Thereby, a gas desorption reaction, e.g., hydrogen fluoride (HF), occurs with the reaction of hydrogen (H2) and fluorine (F). As a result, the amorphous carbon (aC) barrier layer may be peeled-off from the fluorocarbon (CFx) insulating layer or the copper interconnection body due to significant deterioration of their adhesion properties.
To suppress the desorption reaction of hydrogen fluoride (HF), a process for forming an amorphous carbon layer is proposed in Japanese Patent Application Publication No. 2008-141009. In this process the amorphous carbon (aC) layer is doped with a dopant such as silicon (Si). Although the silicon doping of amorphous carbon (aC:Si) layer suppresses the hydrogen fluoride (HF) generation, this process, however, results in generation of silicon tri-fluoride (SiF3), which in turn deteriorates the adhesiveness between the fluorocarbon (CFx) insulating layer and the silicon-doped amorphous carbon (aC:Si) layer. Therefore, the amorphous carbon (aC) layer may be peeled-off from the insulating layer or the interconnection body in the same manner as described previously.
The present invention is proposed in view of the above aforementioned problems. The present invention provides an amorphous carbon (aC) layer forming method to enhance the adhesiveness between an amorphous carbon (aC) layer and a fluorocarbon (CFx) insulting layer while suppressing the fluorination reaction there between.